using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Net;
using System.Runtime.CompilerServices;
using UnityEngine;

namespace Mirror
{
    public static class Extensions
    {
        public static string ToHexString(this ArraySegment<byte> segment) =>
            BitConverter.ToString(segment.Array, segment.Offset, segment.Count);

        // string.GetHashCode is not guaranteed to be the same on all
        // machines, but we need one that is the same on all machines.
        // Uses fnv1a as hash function for more uniform distribution http://www.isthe.com/chongo/tech/comp/fnv/
        // Tests: https://softwareengineering.stackexchange.com/questions/49550/which-hashing-algorithm-is-best-for-uniqueness-and-speed
        // NOTE: Do not call this from hot path because it's slow O(N) for long method names.
        // - As of 2012-02-16 There are 2 design-time callers (weaver) and 1 runtime caller that caches.
        public static int GetStableHashCode(this string text)
        {
            unchecked
            {
                uint hash = 0x811c9dc5;
                uint prime = 0x1000193;

                for (int i = 0; i < text.Length; ++i)
                {
                    byte value = (byte)text[i];
                    hash = hash ^ value;
                    hash *= prime;
                }

                //UnityEngine.Debug.Log($"Created stable hash {(ushort)hash} for {text}");
                return (int)hash;
            }
        }

        // smaller version of our GetStableHashCode.
        // careful, this significantly increases chance of collisions.
        public static ushort GetStableHashCode16(this string text)
        {
            // deterministic hash
            int hash = GetStableHashCode(text);

            // Gets the 32bit fnv1a hash
            // To get it down to 16bit but still reduce hash collisions we cant just cast it to ushort
            // Instead we take the highest 16bits of the 32bit hash and fold them with xor into the lower 16bits
            // This will create a more uniform 16bit hash, the method is described in:
            // http://www.isthe.com/chongo/tech/comp/fnv/ in section "Changing the FNV hash size - xor-folding"
            return (ushort)((hash >> 16) ^ hash);
        }

        // previously in DotnetCompatibility.cs
        // leftover from the UNET days. supposedly for windows store?
        public static string GetMethodName(this Delegate func)
        {
#if NETFX_CORE
            return func.GetMethodInfo().Name;
#else
            return func.Method.Name;
#endif
        }

        // helper function to copy to List<T>
        // C# only provides CopyTo(T[])
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void CopyTo<T>(this IEnumerable<T> source, List<T> destination)
        {
            // foreach allocates. use AddRange.
            destination.AddRange(source);
        }

#if !UNITY_2021_OR_NEWER
        // Unity 2020 and earlier don't have Queue.TryDequeue which we need for batching.
        public static bool TryDequeue<T>(this Queue<T> source, out T element)
        {
            if (source.Count > 0)
            {
                element = source.Dequeue();
                return true;
            }

            element = default;
            return false;
        }
#endif

#if !UNITY_2021_OR_NEWER
        // Unity 2020 and earlier don't have ConcurrentQueue.Clear which we need for ThreadedTransport.
        public static void Clear<T>(this ConcurrentQueue<T> source)
        {
            // while count > 0 risks deadlock if other thread write at the same time.
            // our safest solution is a best-effort approach to clear 'Count' once.
            int count = source.Count; // get it only once
            for (int i = 0; i < count; ++i)
            {
                source.TryDequeue(out _);
            }
        }
#endif

#if !UNITY_2021_3_OR_NEWER
        // Some patch versions of Unity 2021.3 and earlier don't have transform.GetPositionAndRotation which we use for performance in some places
        public static void GetPositionAndRotation(this Transform transform, out Vector3 position, out Quaternion rotation)
        {
            position = transform.position;
            rotation = transform.rotation;
        }

        public static void SetPositionAndRotation(this Transform transform, Vector3 position, Quaternion rotation)
        {
            transform.position = position;
            transform.rotation = rotation;
        }
#endif

        // IPEndPoint address only to pretty string.
        // useful for to get a connection's address for IP bans etc.
        public static string PrettyAddress(this IPEndPoint endPoint)
        {
            if (endPoint == null) return "";

            // Map to IPv4 if "IsIPv4MappedToIPv6" for readability
            // "::ffff:127.0.0.1" -> "127.0.0.1"
            return
                endPoint.Address.IsIPv4MappedToIPv6
                ? endPoint.Address.MapToIPv4().ToString()
                : endPoint.Address.ToString();
        }
    }
}
